The invention concerns an absorbing thin-layer system comprising multiple metallic and dielectric layers.
For a long time, modem techniques of microscopy have included xe2x80x9coptical contrastxe2x80x9d procedures such as dark field, oblique illumination, interference contrast, polarization contrast, relief contrast, and others. These procedures exploit certain physical properties of the microscopic preparation and provide a xe2x80x9ccontrastingxe2x80x9d effect without any injury to the object being examined.
For instance, a Hoffmann modulation contrast system is known from U.S. Pat. No. 4,200,353. This procedure has the disadvantage that undesired color fringes appear because of the undefined phase status of a Hoffmann modulator. Also, disturbing reflections appear in the microscope beam path. They can be reduced by tilting the modulator strongly, but that would require a very demanding mechanical system in the objective lens.
Therefore the objective of this invention is to improve the image properties of a modulator for contrast processes in microscopy, thus avoiding the disadvantages of the known systems.
This objective is attained according to the invention by means of an absorbing thin-layer system comprising metallic and dielectric layers which has a defined phase shift to achieve color-neutral absorption in the visual spectral region, with low residual reflections at the same time. Other advantageous embodiments appear from the subclaims.
The invention is based on the finding that thin layers have a phase-shifting effect which depends on their chemical compositions, their refractive indices and their thicknesses.